The present disclosure relates to a percussion boring system and, more particularly, to an improved leading end assembly for a percussion boring system in the form of a bidirectional cluster hammer reamer (“BCHR”).
A person having ordinary skill in the art understands that horizontal directional drilling systems are capable of directionally boring a winding channel in a substrate. These channels are commonly bored for any number of purposes such as for holding a product in the form of a conductive conduit, a fiber optic cable, a stretch of tubing, a sewer pipe, etc.
Percussion boring a subterranean channel for holding a product usually begins by boring a pilot channel in a substrate along a substantially predetermined path. The pilot channel has an entry point, where the leading end of the horizontal directional drilling system initially enters the substrate, and an exit point where the leading end of the system eventually emerges from the substrate. After the pilot channel is bored, a series of passes back and forth through the channel may be made to expand the channel size and condition its walls in anticipation of installing the product on the final pass.
Devices and methods for expanding a pilot channel vary greatly, and largely depend on the specific subterranean conditions being encountered. Generally, a pilot bore is expanded by either 1) retracting a reaming device and/or 2) pushing a relatively larger percussion bit.
Reaming devices known in the art are relatively simple in design and application—at the exit point of the pilot channel, the percussive bit used to drill the pilot channel is replaced with a slightly larger reaming device that is simply dragged back through the pilot channel when the drill string is retracted. In most applications, reamers work well to expand and condition a pilot channel. The advantage of reamers known in the art is that they can be pulled through a pilot channel by a retracted drill string, thereby alleviating any requirement for steering by the operator. The disadvantage of reamers known in the art, however, is that they are limited in the amount of channel expansion they can provide per pass.
An advantage of using percussive devices to expand a pilot channel is that percussive devices may provide for a relative increase in the amount of bore expansion that may be realized over a single pass when compared to a reamer. Just like the percussive bit used to bore the pilot channel, percussive devices used to expand the pilot channel are really just relatively bigger percussive bits capable of powering through rock and dirt. The disadvantage of using a percussive device for pilot channel expansion, however, is that the operator must take care to stay on the path of the pilot channel and not inadvertently bore off course. As one of ordinary skill in the art would understand, reaming devices stay on course by virtue of being pulled back through the channel, but percussive devices known in the art must be steered as they are “pushed” through the channel.
Therefore, systems and methods known in the art for expanding a subterranean pilot channel suffer from either a limited ability to expand a pilot channel as they are retracted or from the requirement that they be steered along the pilot channel as they are pushed. As such, there is a need in the art for a percussive boring system that may be pulled or retracted through a pilot channel so that the expansion of the pilot channel is optimized without the requirement that the system be steered.